Large structures such as those mentioned above are traditionally manufactured using large fixed-based machines such as robotic drilling machines and riveting machines. Some of the well-known drawbacks of using such machines include the high initial capital investment to acquire and install the equipment and the large and expensive foundations that they require, the significant amount of time and resources required for training workers how to operate the complex machines and for maintaining and supporting the machines, and the loss of productive use of the machines during certification, qualification, and maintenance of the machines. Additionally, large fixed-based machines do not lend themselves to Continuous Flow Manufacturing (CFM), which is considered by most leading manufacturing experts to be the most efficient manufacturing method. Furthermore, manufacturing of large structures such as airplane structures has conventionally required model-specific tooling such as floor assembly jigs (FAJs) and Gemcor header systems. Such model-specific tooling represents a substantial fraction (e.g., about one-third) of the total cost of developing a new airplane.
Because of disadvantages such as those mentioned above, alternative manufacturing methods that avoid one or more of these disadvantages are desirable. Preferably, the methods should be capable of supporting a CFM process, and should facilitate off-line maintenance and qualification of a machine while another replacement machine continues production, and hence a system employing non-fixed-base machines is needed. Although these goals are desirable, they have been difficult to achieve for various reasons, not the least of which is the difficulty of accurately positioning non-fixed-base machines relative to the workpiece. Systems such as laser positioners can be used for positioning machines relative to the workpiece, but such systems are highly complex and usually require set-ups that are specific to the particular workpiece being manufactured, and are often limited by line-of-sight considerations.